1. Field of the Invention
The present invention relates to an antenna structure for communication, which is especially suitable for a base station (BS) in the radio communication system as a signal transceiver between the base station and mobile terminals to increase the half-power beamwidth in the H-plane.
2. Related Art
Nowadays, the mobile phone has become an essential communication tool in our everyday life and tends to become more popular. The usage of the mobile phone is very similar to that of the conventional telephone. The signal transmission of the mobile phone is duplex so that persons can talk to each other simultaneously. And in order to protect personal privacy, every mobile phone customer has an exclusive phone number and can talk to somebody in coded format via the base station.
Nevertheless, the most popular communication scheme used in the current base stations is the cellular scheme, wherein the high power transmitter for each communication region has been replaced by a lot of low power transmitters, which are also called cells, spreading over the same region. Therefore, in order to cover the communication region throughout and obtain good signal quality, it is necessary to set up a great numbers of cells. And the transmission power, horizontal angular range, and vertical angular range of the base station have also become important parameters to improve the signal quality. If the total amount of antenna can be reduced as low as possible while covering even wider transmission and reception region, the economic profit would be greatly increased.
FIG. 1 shows a three-dimensional structure sketch of a conventional antenna, which comprises:
a slot coupled a microstrip patch 20, made of a low-loss dielectric flat plate, wherein there is a microstrip 21 on the back plane and a slot 22 on the front plane. The patch is connected to a signal source, which is not shown in this figure, via a conducting line 40; PA1 a reflector 30, which is a metal plate attached to the back plane of the slot coupled microstrip patch 20 in the manner of electrical isolation so that the backward radiated electromagnetic waves would be reflected forward; and PA1 an antenna combination 10, placed in front of the slot coupled microstrip patch 20 in the manner of electrical isolation so as to increase the radiation power of the electromagnetic waves. The antenna combination 10 comprises a front-plate 11a and a patch 11b, which are both connected to the slot coupled microstrip patch 20 in parallel and in the manner of electrical isolation. The areas of the patch 11b and the front-plate 11a are the same so as to increase the radiation power of the electromagnetic waves. PA1 a front-plate, which comprises a first flat plate, a second flat plate, and a curved plate, which is used to connect the first flat plate and the second flat plate. The first flat plate and the second flat plate are placed in the same plane and electrically connected to the curved plate; and PA1 several patches, parallel to the first flat plate and the second flat plate, and the connection between the front-plate and the patches is electrically isolated. The area of each patch is the same as the projected area of the front-plate onto the patch so as to increase the radiation power of the electromagnetic waves.
By using the above antenna structure to transmit signals, the horizontal transmission angle .theta. will be limited within the range of 60.degree. to 70.degree. from center, or 80.degree. at maximum. Therefore, as far as this rectangular antenna structure is concerned, it is very difficult to satisfy the demand of large signal transmission and wide reception range.